TL;DR
Erratic motion on the R-2000iC is most often a worn or intermittently open cable in the arm harness. Inspect the cable bundle at J1 and J3 first as those points see the most flexing.
What you might see
- robot arm jerks or twitches during a programmed move
- path is not repeatable between cycles
- controller reports communication or cable fault
- motion error increases when the arm is at full extension
Likely causes
Worn or chafed internal cable harness causing intermittent encoder or power signal loss
Loose connector on the encoder feedback cable causing erratic position signals
Encoder fault on the affected axis producing spurious position data
Electromagnetic interference from nearby welding or variable frequency drives
Required tools
- FANUC R-30iB controller access (alarm screen)
- LOTO kit
- Flashlight (for cable inspection)
- Connector pin extraction tool (for pin inspection)
- Multimeter (continuity test on suspect cable)
Safety first
- Lock out the robot controller before handling any cable on the robot arm. An energized arm can move unexpectedly if an encoder signal is restored during handling.
- Never enter the work envelope without locking out the controller. The erratic motion condition makes the robot especially hazardous.
- Use T1 mode (restricted speed, deadman active) for any jogging done to reproduce a fault.
Procedure
- 1
Check the FANUC controller for encoder or communication alarms. Note the axis and alarm code.[1]
- 2
Lock out the robot controller. Visually inspect the external cable bundle along the arm from J1 base to the wrist. Look for cuts, abrasion through the jacket, or pinch points.[1]
- 3
Flex each section of the cable bundle gently by hand while watching the controller for alarm triggers. An intermittent connection will trigger an alarm during flexion.
- 4
Inspect all connectors at the J1 base panel, J3 upper arm junction box, and wrist. Look for backed-out pins, corrosion, or loose locking rings.
- 5
Re-seat all connectors and re-torque any locking rings to the FANUC specification. Re-test with a controlled jog cycle.
- 6
If the fault follows a specific axis and is not resolved by connector re-seating, the internal harness for that axis needs replacement. This is a FANUC-service-level repair.
- 7
Check the cable routing for contact with sharp edges, clamps too tight, or cable bend radius below the FANUC minimum.
- 8
If interference from nearby equipment is suspected, verify the robot controller cabinet is properly grounded and all shielded cable grounds are connected at one end only.
Sources
FANUC R-2000iC Robotic Arm Maintenance Manual, FANUC
FANUC R-2000iC Robot Maintenance Manual, cable harness inspection and replacement procedures (general)
View source
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